Diffusers Demystified Article

Thanks so much for writing this article! It was an awesome primer to start me out, but where do I go to learn even more in depth about aero? Is there an automotive aero text book? or is it mostly guarded secrets of F1 that have trickled down a little?

Glad you enjoyed it. We've done aero articles in the past, but does this mean you want more? Fortunately Steve, who wrote that piece, is awesome to work with. Plus he comes from our world.

Check out these books: Competition Car Aerodynamics by Simon McBeath Race Car Aerodynamics: Designing For Speed by Joseph Katz

Also read racecar engineering for several years. They always seem to have something really cool in each issue that I pick up.

Durty, you could always post questions on the forum.
I lurk alot, but post a little bit too, when I'm not actually doing aero work.
Dave, thanks for the props.
The books listed are a pretty good start and are readable for getting started.

Thanks, Steve Stafford.

stafford1500 wrote: Durty, you could always post questions on the forum. I lurk alot, but post a little bit too, when I'm not actually doing aero work. Dave, thanks for the props. The books listed are a pretty good start and are readable for getting started. Thanks, Steve Stafford.

Steve - how does one test / troubleshoot the efficiency of a home built diffuser?

For wings and other "top side" things like nose/hood "slickness" and so on I tape string to half of it and point my camera - it either sticks or flutters but aside from that - I struggle to determine what works or what just feels good. Sometimes "feels good" is enough to be able to build confidence and push harder but quantifying it would be nice. Is there a simple trick for evaluating these that does not involve smoke in a wind tunnel? Things like rubber bands on the damper shaft to measure compression never seem consistent enough to be more than noise (tried it with a wing/splitter combo).

David S. Wallens wrote: Glad you enjoyed it. We've done aero articles in the past, but does this mean you want more?

Yes. I would like to learn to practice these black arts.

GPS, You could use the tufts and camera method on the diffuser as well. Same basic analysis, if the strings are pointing to the back, you got it right. If the are falling down or pointing to the front or sides, you have too much expansion. Getting 'real' data would be more difficult. Since downforce and drag are a funtion of speed squared testing on the road is not an easy proposition. Seat of the pants is going to tell you alot about where you make downforce, since you feel the balance shift more than the actual downforce change.

stafford1500 wrote: Since downforce and drag are a funtion of speed squared testing on the road is not an easy proposition. Seat of the pants is going to tell you alot about where you make downforce, since you feel the balance shift more than the actual downforce change.

I suppose I could rig a camera to see it from the back bumper without putting it directly in the air flow itself... most of my "testing" happens at NJMP, Watkins Glen or Summit Point so I can see improvement in lap time and top speed pretty well but it is really hard to tell if a change was good or bad because it was better downforce or the downforce + drag was just more "comfortable" and allowed me to drive harder for a better lap time while actually being less efficient. Seat of the pants is my main tuning fork but it has lied to me before.

I run data but it is only 3-axis accel and GPS laptime - and I make inferences from it about what works. I just never know why.

and I thought aero bits were stuck on a car so drifters could shed them all over the track...............

so, yes, I'm dragging this up... mainly thanks to seeing it via the new aero-subforum.  props to all involved on that.

considering the discussion that's happened on the "make a wing out of plywood" thread, where a number of people have expressed interest in knowing more about diffusers... and there being a bunch of new user/readers that have come on since that article was written.  I'd suggest that this article be consider for "digitization" and release into the articles section.  That article and the forum thread connected to it (i.e. not this one) would probably be the right place to start.

In reply to sleepyhead :

Yes, yes, yes, please!

Also, any word on the Genesis of this new forum section? I was surprised to see it but am happy it's here!

GPS, the other way would be to use a series of pressure sensors. The pressures we're dealing with are in the same range as building HVAC static pressure, so they'll be available used/surplus/from Arrow. If the pressure in the diffuser isn't steady and rising as you go from front to rear, then part of the diffuser is stalled.